Olefin polymers such as polyethylenes and polypropylenes are produced by use of a transition metal polymerization catalyst thereby leaving small amounts of catalyst residues in the polymer. Such residues are typically deactivated after the polymer leaves the polymerization zone, because otherwise undesired polymerization reactions and other undesired reactions may occur outside the polymerization zone, especially when the polymerization mixture is subjected to higher temperatures. Higher temperatures especially occur in solution or high pressure polymerization processes where the temperatures of the polymerization mixture leaving the reactor may be well above 100° C. Undesired polymerization causes formation of low molecular weight oligomers, waxes and greases or otherwise changes polymer properties in an uncontrollable manner. In addition, polymerization outside the reactor can lead to excess heat generation and deposits of relatively low molecular weight polymer especially in recycle lines and vessels. Polymers are also subjected to high temperatures when melt processing the polymers, such as in pellet extrusion or other extrusion or molding operations to make articles.
It is known to add water and other polar compounds or reactive hydrogen containing compounds at the end of a polymerization reaction to deactivate the polymerization catalyst. Upon contact of such compounds with the catalyst, considerable amounts of acidic compounds and halide containing compounds such as hydrogen chloride may be formed which cause corrosion in the process equipment and can enter into monomer or diluent recycle lines and thus need to be rendered inactive. Therefore, besides a deactivator compound also a compound is added that converts or traps the acidic and halogen-containing compounds into non-harmful compounds which can remain in the polymers. Compounds of a basic nature, and particularly metal salts of aliphatic or fatty acids such as calcium stearate and natural or synthetic hydrotalcites are typically used for this purpose. EP-67,645 and EP-71,252 disclose the use of water in combination with a fatty acid salt in a hydrocarbon, wherein the fatty acid salt may act to neutralize acids formed by the water-catalyst reaction.
The use of an aliphatic acid metal salt in the process may result in build-up of reaction products, such as aliphatic acids, e.g. fatty acids, in the recycled monomers and process diluent thereby leading to reduced polymerization rates and additional cost in cleaning up recycle lines. In addition, during processing at high temperature the corresponding aliphatic acid may migrate through the polymer and sweat out of the polymer onto processing equipment resulting in reduced processing and product performance, and requiring cleaning of equipment. Further, the aliphatic metal salts are not readily miscible with or dissolvable in polymer process streams under process conditions and as such are not very effective and need to be added in relatively large amounts, which also increases the production cost.
GB-2132214 discloses a process for polymerizing one or more 1-olefins at a pressure of at least 500 bar and at a temperature in the range of 150–320° C. wherein the polymerization catalyst is deactivated by adding a deactivating agent comprising a polyalkylene glycol, a polyvinyl alcohol or an aliphatic alcohol containing at least 10 carbon atoms.
EP-140131 discloses deactivation of catalyst systems comprising a transition metal compound and an organic aluminum compound in ethylene polymerization processes at pressures of 300 to 3500 bar and temperatures from 150 to 350° C. using polyglycols.
WO-92/14766 discloses the use of a combination of a non-volatile and a volatile catalyst killer in high pressure processes. Water or water-releasing compounds are disclosed as volatile catalyst killer. The non-volatile killer components may be a component with a molecular weight higher than 200, such as alcohols, phenols diols, polyols, saccharides, ethers, epoxides, aldehydes, ketones, carboxylic acids, diacids and polyacids, their anhydrides, esters or salts, polyalkylene glycols, and amines.
It is an objective of the present invention to provide for an additive composition that can render a transition metal polymerization catalyst or its decomposition products inert after the polymerization step or during conversion or use of the polymer, thereby avoiding significant corrosion problems in the process or conversion equipment. According to a further objective the present invention provides for the use of an additive composition that renders transition metal catalysts or its decomposition products inert without releasing unacceptable amounts of acidic byproducts.
It is another objective of the present invention to provide for an additive which can remain in the polymer and of which the reaction products can remain in the polymer without negatively influencing the product properties.
It is a further objective to provide a process in which problems of post reactor polymerization are reduced or eliminated.
According to yet another objective an additive composition is provided that reduces or eliminates the plating out of compounds from the polymer on processing equipment during high temperature conversion of the polymer.